HTT and Huntington disease: Peripheral involvement in HD pathology is known from preclinical (e.g., Ciammola et al. 2006; Zielonka et al. 2014) as well as clinical research and mostly attributed to disruption of cellular mechanisms (e.g., energy metabolism) by neurodegeneration, dysfunctional mutant HTT-protein itself or its aggregates (Carroll et al. 2015; Turner et al. 2007).